This research proposal is to establish the macaque monkey as a model for studying normal primate hematopoiesis. During years 1-3, the distribution of lymphocyte subsets within bone marrow, lymph node, spleen, and peripheral blood compartments will be compared and the maturation and turnover of specific subsets of cells will be assessed using cell cycle analysis and dual fluorescence flow cytometry. These techniques, together with assays to assess maturation of cells of the monocytic/granulocytic series will be employed to study the hematopathology associated with type D retrovirus and SIV infection of macaques. Studies during years 4 and 5 will extend the observations on mechanisms of virus induced hematopathology and begin to explore domestic species as models for hematopoiesis.